The goal of this proposal is to prepare the candidate, Molly Magill, Ph.D., for a career as an independent clinical scientist specializing in the study of mechanisms of behavior change in psychosocial treatment for alcohol use disorders. Dr. Magill is a clinical social worker who has focused her career on substance use treatment at the level of science and practice. The candidate's experiences to date have led to a belief that research on change mechanisms can enhance the knowledge that is gained from clinical trials research. This is the case for findings of treatment outcome equivalence or difference. Such information can lead to greater treatment efficiency by identifying common treatment factors, treatment-specific ingredients, and thus, dissemination priorities. Dr. Magill has a beginning foundation in this area of research, but there are important gaps in her academic and research training. With advanced training in: (1) the design of change process research with an emphasis on observational measurement development and (2) the statistical analysis of change mechanisms with an emphasis on longitudinal methods, Dr. Magill will contribute to this area of study and to the improvement of psychosocial treatment for alcohol use disorders. The proposed Training Plan will occur at the Brown University Center for Alcohol and Addiction Studies under the mentorship of Dr. Robert Stout, with co-mentorship provided by Dr. Richard Longabaugh and Dr. Timothy Apodaca and consultation provided by Dr. Kathleen Carroll and Dr. Carlo DiClemente. The proposed Research Plan will directly apply skills that arise from training activities. Specifically, it will employ observational coding methods on longitudinal Project MATCH session data to inform knowledge of within-treatment mechanisms in aftercare for alcohol use disorders. The proposed Primary Aims will examine the construct of behavior change language (statements of commitment, ability, taking steps) with two novel sub-dimensions (regarding drinking, regarding coping) that are expected to be particularly useful for modeling common factor hypotheses about client post-session proximal and distal change behavior. The proposed Secondary Aims will draw from the general psychotherapy and addictions literature to examine two therapist common factor predictors (support of client self-efficacy, skills focus) of client mechanisms. The proposed Research Plan is well integrated with the proposed Training Goals, it has the potential to inform clinical practice, and it will ground subsequent research on common factors of client proximal and distal behavior change in treatment for alcohol use disorders.